The proposed sale of the Harpoon systems "will help improve the security of the recipient and assist in maintaining political stability, military balance... and progress in the region," the State Department said in a statement.

The deal involves 100 Harpoon Coastal Defense Systems (HCDS), which includes 400 RGM-84L-4 Harpoon Block II Surface Launched Missiles with a maximum range of 75 miles (125 kilometers).

The missiles, manufactured by Boeing, can be positioned on fixed platforms or mounted on trucks.

Democratic and self-ruled Taiwan lives under constant threat of invasion by authoritarian China, whose leaders view the island as part of their territory.

They have vowed to one day seize the island, by force if necessary.

Beijing has ramped up diplomatic and military pressure on Taiwan since the 2016 election of President Tsai Ing-wen, who views the island as a de facto sovereign nation and not part of "one China."

Chinese fighter jets and bombers have entered Taiwan's air defense zone with increasing frequency in recent months, while propaganda films have shown simulated attacks on Taiwan-like territories.

Last Wednesday, the US said it had approved the $1 billion sale of 135 precision-guided, air-launched AGM-84H SLAM-ER cruise missiles -- which unlike the Harpoon have a range greater than the width of the Taiwan Strait that separates the island from mainland China.

In response, Beijing on Monday said it would impose sanctions on Lockheed Martin, a Boeing defense division and other US firms involved the arms sale.

Chinese foreign ministry spokesman Zhao Lijian said the sanctions were "to safeguard national interests" and would apply to those who have "behaved badly in the process of arms sales to Taiwan."

Zhao did not give further details on the sanctions.

Under the administration of President Donald Trump the US has brought Taiwan into play as part of a wider diplomatic and economic squeeze of rival China, sending high-level envoys and boosting arms sales.